Ion-trap cathode-ray tube



May 5, 1953 K. A. HOAGLAND ION-TRAP CATHODE-RAY TUBE Filed Nov. 25, 1949 INVEN TOR. KENNETH A. HOAGLAND Patented May 5, 1953 ION-PEA? OATHODE-RAY TUBE Kenneth A. Im gined, New'ark N. assgg'norft'o Allen B. Du Laboratories, The, Pa-seats, N. J a col'poration'cf nelawsre Application-November'zi 1949, Serial No. 129,260

9 "Claims. 1 c

Thisinvention-r-elates to cathode-ray tubes and more particularly to the ion trap used in -mag netically deflected cathode-raytubes. H

It is known tc employ a bent electrode in the electron-gun of -a cathode tub e as amea s for trapping the negati-re-ions-emitted by the cathode and contrcl grid. Hereto-fcre the sc-calleel bent gun type ion-trap has resulted in an unwielclyaud impractical structure from the commercial standpoint.

It is one object of my invention to "obtain an improved cathode-ray tube.

A second object is to obtain a bent-gun ion-trap type tube cfft'he samesize and shape and'havihg the same iiefiecticn and rocussing characteristics as a straight-gun'tube. I

V Other objects wilibea'ppare'nt from the specificatioris and drawings in which:

Figure 1 isacross-setiohal View o'f a cathoderay "tube ein'bodying this iiiveiition and showing the operating electron and. ion beams. v

Figure 2 shows, in cross-sectional view, a cathode-ray tube havihg a prior 'art'ti pe of electron gun to illustrate the "nature of operation thereof.

Figure 1 shc'ws a. cathod'e iaiy'tub'e l cohtaiiii'ng an electron gun comprising a heater 2 inside a cathode thimblelwhidh has an electron ini'ssiiie coating on a portion thereof and is partially "or completely enclosed within a control grid "electrode i. Adjacent the control "grid 4 is a first anocl'e'o'iscreen grid electrode "6, also referredftc and known as "the se'ccncigrid, which has the shape'of a shallow cup and is preferably tr the type "disclosed in cclpeinding U. S. app'licaticn Serial No. 91,714, by 'Pohle eta]. An elec'trod'e "i, which is sometimes ltriowh as fasecond anoue but which may be properly idelitifiedsihiply asahhde, completes the electrcnsun structure.

As may be seen inFigure 1 of the drawing, the control grid-Q and screen grid 9 have the same diameter as the anode I.

The anode E has a'naperture discll near the outer end thereof, 1. e. the end more distant om the screen grid. 6. The openihgin the-disc! is generally termed the limitingaperture. The end of the anode *5 adjacent thetiisc-liis pai'tieill-ysupportedby a device 8 known as a spider, which has sprihg fingers bearing on an electrically eons-c tiv'e coating 1 i and making electrical contact therewith. This coating H isa'pplied to the walls of the cathode-ray tube I and extenm rema proximately the ends of the fingers of the spider 9 to the large end ofthe cathode-ray tube l, near the fiuc'rescerit screen HZ.

*Othe'r components essential to 'therior'mal operation of the cathcde ray'tube Fbutrioth'stially ccinstructee. integrally therewith are the ibn ti'ap magnet 1'3, the focus 0011 M anti-the deflection yoke Hi.

In operation, am electric current assm'g through the heater causes hea-t, thereby raising the temperature of the emissive coating on the cathode 3 to the temperature at whichelectrons are emitted. Negative-ions are also emitted along With the electrons. There is reason to believe that at least a portion of these ions originate at the cathode '3 flue to the-chemical breakdown cf the enii'ssive material, and the present invention'will beillustrated with reference to these 'icri's.

I Since these ions are emitted along with "the el'ect'roiis anti have "the same electrical charge, they react to electric field's in the same Way as e'lb'fiiblls. However, since the mass of an 'iOil is m"ar:y'times "gr ater than "that 'o'f'ah election, the ions are not. deflected by magnetic fields nearly as'a'r'e *the'eiectrons. The inns emitted from the'ca'thoee 3 are cc'nstrrctcd into "narrow bufidie'anirpass thr ugh the'aperture in the controlgrid iafter which'thebu'helle starts to spread out. Because of the electric fieitl between the screen grizit anutheancrie t, 'a'partiai focussing action 'i'sekerteii onth'eions which restricts "them to fa comparativiy small bundle it. Substantially a11-'of1th'e ions ii this buiidlear'e caught by thes'iire'of theanoiie '1 While the electrons form mg a seam IE are 'defiected'by the'ion-trapih'agnet #3 and passoxit throughthe limitingaperture ih'the disc "8 to be iocussed "by the focus'sing "coil defiieictedbythe deflection yoke it. l i-gure 2 'ill"l strates"the operation of a prior art type or cathode-ray tube in which "the ion-trapping occurs'in-"the electrode followihgthecontrol grid. in thiscase theftiibe-is a ftriodetypefi iv e. there no screen so th'atthe auche "Reorresponfi'iiig' to the aho'cle fi n Figure "1 is the-electr'edefollowihg'the coritrfil elidi. Allo'f the corn-- poneiits in Figure 2 are labelled Withthe same reference characters similar components in Figure Jtii1a37-'be"seenin Figure that, Withoutthc fiai tial fcciiss'ing acti-on-of the screen or sece'ricl gtiii 8, the ihh beam Pi spreads over 'a ihuc'h larger-angle. s'o'fneof theions gc through the limiting 'aga ture'in the ciisc 2! and strike the screen 21 causing th'e well lhown iolnblemishes. 1

In order *to preven t these blemishes in this atlioderaytube it l ms heretofore been necessary either to increase the iength or the barrel of the anodelmhichresulh in a greate'rcve'raH length for the tube, or to increase the an'g1e A "of the bend, which necessitates a thicker neck for -'the cei'thode ray tube. B'othof these solutions are un desirable becauseofa strong commercial teniiency touse the smallestipos'sibl'e cathode-ray tube cemmensurate with a desired screen 1 area.

"That-mm magnetically defle'cted tube'as used herein 'refers to 'th'e type "cathode ray tube censt'r'ucted fora'nd intended to 'be used with edditioiial 'm'a'g'netic beam deflection means as contrusted, -=-fo'r 1 instance, with "electrostatic type de flection tube. The term "magnetically focussed tube means that tube constructed for and intended to be used with magnetic focussing means for the electron beam, although it is contemplated that some electrostatic focussing may also be involved, as contrasted with tubes having built in electrostatic focussing means.

I have described this invention in terms of a specific embodiment, but it will be apparent to those skilled in the art that it is possible to make modifications within the scope of the following claims.

What is claimed is:

1. A magnetically focussed, magnetically defiected cathode-ray tube comprising a cathode; a control grid; a screen grid; a fluorescent screen; and a tubular anode, said tubular anode having an axial bend with the tubular portion on one side of said bend directed substantially at the center of said screen and the tubular portion on the other side of said bend aligned substantially coaxially with said cathode, control grid and screen grid.

2. A magnetically focussed magnetically deflected cathode-ray tube comprising a straightnecked vessel containing a cathode; a control grid; a screen grid; a fluorescent screen; and a tubular anode, said tubular anode having an axial bend with the tubular portion on one side of said bend substantially in axial alignment with the longitudinal axis at said tube and the tubular portion on the other side of said bend aligned substantially coaxially with said cathode, control grid and screen grid.

3. A magnetically focussed magnetically deflected cathode-ray tube comprising a cathode; a control grid; a shallow, cup-like screen grid electrode having a substantially circular end portion with a central aperture therein, said cathode, control grid and screen grid having a common axis; said tube having a fluorescent screen; and an anode composed of two substantially tubular portions having intersecting axes, the axis of one of said tubular portions being directed at said screen and said other tubular portion being coaxial with said cathode, control grid and screen grid.

4. A magnetically deflected cathode ray tube comprising an evacuated vessel having a bulb portion and a straight cylindrical neck portion, an electron gun mounted in said neck portion, said gun comprising a cathode, a control grid, a second grid, and a tubular anode arranged in order along the path traversed by the electrons emanating from said cathode, said anode having a centrally apertured conducting disk mounted transversely therein, said electron gun being positioned in said neck portion so that a straight line from the center of said cathode through the center of said aperture intersects the axis of said neck at an angle.

5. A magnetically deflected cathode ray tube comprising an evacuated vessel having a bulb portion, an end wall on said wall portion and a straight cylindrical neck portion opposite said end wall, said neck portion having a conductive coating over a portion of the inside wall thereof with the axis of said neck being substantially:

perpendicular to the plane of said end wall, an electron gun mounted in said neck portion, said gun comprising a cathode, a control grid, a second grid and a tubular anode having a centrally apertured disk transversely mounted therein, the aperture in said disk being coaxial with said neck portion, said electrodes being arranged in order along the path traversed by electrons emaw nating from said cathode, said electron gun being positioned in said neck so that a line from the center of said cathode coaxial with said control grid and said second grid intersects at an angle a line coaxial with said neck through the center of said aperture.

6. A tube in accordance with claim 4, in which said control grid is closer to the side wall of said neck portion than said conducting disc in said anode.

7. A magnetically deflected cathode ray tube comprising an evacuated vessel having a bulb portion and a straight cylindrical neck portion, an electron gun mounted in said neck portion, said gun comprising a cathode, a control grid, a second grid and a tubular anode arranged in order along the path traversed by the electrons emanating from said cathode, said anode having an apertured conducting disc mounted transversely therein, said second grid and said anode having substantially the same diameter, said electron gun being positioned in said neck portion so that a straight line from the center of said cathode through the center of said aperture intersects the axis of said neck at an angle.

8. The tube in accordance with claim 7, in which said control grid and said second grid have tubular portions, said tubular portions being of substantially the same diameter as said anode.

9. A magnetically deflected cathode ray tube comprising an evacuated vessel having a bulb portion including a target and having a straight cylindrical neck portion, an electron gun mounted in said neck portion, said gun comprising a cathode; a control grid; a second grid; and a tubular anode arranged in order along the path traversed by the electrons emanating from said cathode, said anode having an apertured conducting disc mounted transversely therein, said electron gun being positioned in said neck portion so that a straight line from the center of said cathode through the center of said aperture intersects the axis of said neck at an angle, said second grid and said anode providing an electrostatic focusing field therebetween to partially focus ions and electrons produced by said gun, into a beam; a magnet located adjacent the path traversed by said electrons and producing a magnetic field to deflect the partially focused beam of electrons; and means providing a second focusing field in the region of said aperture to focus only said electron beam on said target.

KENNETH A. HOAGLAND.

1946, vol. 18, pages 385-386.

The Negative-Ion Blemish in a Cathode-Ray Tube and Its Elimination, by R. M. Bowie, Proceedings of the Institute of Radio Engineers, vol. 36, No. 12 (pages 1482 thru 1486), December 1948. 

